FIG. 10 shows a differential including a differential case 3 to which the rotation of a final drive gear 1 of a transmission is transmitted through a final driven gear 2, which is supported by the differential case 3, a pair of pinions 5 fixed to respective pinions shafts 5, side gears 6a and 6b which mesh with the pinions 5, whereby rotation of the differential case 3 is transmitted to the side gears 6a and 6b through the pinions 5, and then to left and right axles 7a and 7b which support the side gears 6a and 6b, respectively. The differential case 3 has tubular portions 8a and 8b as shafts on both sides thereof which are rotatably supported by a pair of bearings B, respectively, which are supported by a housing 9.
The final driven gear 2 of the differential, which is supported by the differential case 3, is a helical gear. Thus, when the final driven gear 2 rotates, thrust loads act on the differential case 3.
In order to receive such thrust loads, tapered rollers bearings are used as the bearings B supporting the differential case 3 to rotatably support the differential case 3.
A helical gear is also used in an automotive transmission to transmit torque. Thus when a shaft supporting this helical gear rotates, radial loads and thrust loads act on the shaft supporting the helical gear.
Thus, a tapered roller bearing is used to support a shaft supporting a bevel gear in an automotive transmission too.
But since tapered roller bearings are large in load bearing capacity and thus torque, which tends to increase fuel consumption. In order to improve fuel economy, deep groove ball bearings should be used instead because deep groove ball bearings are lower in torque loss.
Deep groove ball bearings comprise an outer race, an inner race, balls mounted between the inner and outer races, and a retainer retaining the balls. The retainer may be made of a metal or may be made of a synthetic resin as disclosed in Patent document 1.